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| #39951 (Received by flhurricane at: 4:34 AM 16.Aug.2005) TCDAT4 HURRICANE IRENE DISCUSSION NUMBER 47 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 5 AM EDT TUE AUG 16 2005 WHILE THE OVERALL CONVECTIVE CLOUD APPEARANCE HAS CHANGED LITTLE DURING THE PAST 6 HOURS IN INFRARED SATELLITE IMAGERY...SEVERAL SSSMI...AMSU...AND TRMM MICROWAVE OVERPASSES HAVE SHOWN A GRADUAL DEGRADATION IN THE INNER CORE CONVECTIVE FEATURES AND EYE STRUCTURE. A DISTINCT EASTWARD TILT OF THE EYE WAS NOTED IN 0447Z AND 0625Z TRMM OVERPASSES...ALTHOUGH THE LATTER IMAGE SUGGESTED THAT LESS TILTING OF THE EYE WAS OCCURRING AS COMPARED TO EARLIER PASSES. SATELLITE INTENSITY ESTIMATES ARE T4.5/77KT FROM BOTH TAFB AND SAB. GIVEN THE RAGGED EYE APPEARANCE NOTED IN THE MICROWAVE DATA...THE INITIAL INTENSITY HAS BEEN DECREASED TO 75 KT. THE INITIAL MOTION ESTIMATE IS 090/08 BASED ON THE LAST 6 HOURS OF MICROWAVE SATELLITE POSITIONS. THE EASTWARD MOTION IS LIKELY DUE TO A SHORTWAVE CAUGHT UP IN THE FASTER WESTERLIES WELL TO THE NORTH OF IRENE THAT IS BYPASSING THE CYCLONE. THIS HAS RESULTED IN WEAKER WESTERLY STEERING FLOW ON THE SOUTH SIDE OF AN EAST-WEST ORIENTED JETSTREAM. HOWEVER...A MUCH STRONGER AND HIGHER AMPLITUDE SHORTWAVE TROUGH OVER THE EASTERN GREAT LAKES AND OHIO VALLEY REGION IS EXPECTED TO MOVE QUICKLY EASTWARD AND GRADUALLY LIFT OUT IRENE TO THE NORTHEAST BY 36 HOURS...AND THEN RAPIDLY ACCELERATE THE CYCLONE BY 48 HOURS. BETWEEN 36-48 HOURS...IRENE WILL BE MOVING OVER SUB-24C SSTS...SO TRANSITION TO A POWERFUL EXTRATROPICAL LOW PRESSURE SYSTEM IS EXPECTED. DUE TO THE MORE EASTWARD INITIAL POSITION...THE OFFICIAL FORECAST TRACK IS A LITTLE TO THE RIGHT OF THE PREVIOUS FORECAST...AND IS CLOSE TO THE NHC MODEL CONSENSUS. THE INITIAL EASTWARD MOTION WILL KEEP IRENE OVER WARMER WATER A LITTLE LONGER THAN PREVIOUSLY EXPECTED...BUT A GRADUAL INCREASE IN THE WESTERLY VERTICAL SHEAR WILL LIKELY OVERCOME ANY POSITIVE CONTRIBUTION FROM THE 28C SSTS. ONCE IRENE HITS THE ICY WATERS OF THE NORTH ATLANTIC IN ABOUT 48 HOURS...ANY REMAINING TROPICAL CHARACTERISTICS SHOULD QUICKLY DISAPPEAR. HOWEVER...WITH SUCH A STRONG SHORTWAVE TROUGH AND JETSTREAM APPROACHING...THE INCREASING BAROCLINIC ENERGY SHOULD KEEP IRENE A RATHER POTENT EXTRATROPICAL LOW PRESSURE SYSTEM OVER THE FAR NORTH ATLANTIC. FORECASTER STEWART FORECAST POSITIONS AND MAX WINDS INITIAL 16/0900Z 36.7N 63.5W 75 KT 12HR VT 16/1800Z 36.9N 62.0W 70 KT 24HR VT 17/0600Z 37.8N 60.1W 65 KT 36HR VT 17/1800Z 39.8N 56.7W 55 KT...BECOMING EXTRATROPICAL 48HR VT 18/0600Z 44.6N 50.1W 50 KT...EXTRATROPICAL 72HR VT 19/0600Z 53.6N 37.8W 45 KT...EXTRATROPICAL 96HR VT 20/0600Z 59.0N 31.0W 45 KT...EXTRATROPICAL 120HR VT 21/0600Z...ABSORBED BY FRONTAL SYSTEM |
